In the fabrication of semiconductor wafers, a plurality of wafers is usually disposed in a stacked, spaced apart relationship within a sealed carrier or pod having a door openable on one face of the carrier. The carrier when sealed provides a substantially contaminant-free environment for the wafers disposed therein, and these wafers can be moved within the carrier to various intended positions for processing into semiconductor devices or circuits. Often the wafers are stored in a cassette which is itself retainable in the carrier. The cassette is removable from the carrier for transferring the wafers from the carrier to the processing equipment. The carrier and cassette can maintain the wafers either horizontally or vertically.
In cassette-based systems, when the carrier is installed in position on processing apparatus, the carrier door is opened and the cassette within the carrier is removed from the carrier by a robot arm or other suitable transfer mechanism to a position at which one or more wafers can be removed from the cassette for conveyance to intended positions for subsequent processing. This motion typically involves a translation of the cassette out of the carrier along a straight line, either vertically or horizontally, and then a rotation of the cassette to a position in which the wafers are accessible to the processing apparatus. In similar fashion, wafers can be loaded into respective slots of the cassette and the cassette when fully loaded can be moved into the carrier by a rotation followed by a translation. The rotation of the wafers occurs over a separate area of the floor space than the translation of the wafers, thereby increasing the overall footprint of the device.
Recently, the semiconductor industry has begun manufacturing larger wafers having a diameter of 300 mm. Additionally, cassetteless carriers for these larger wafers are being introduced. These carriers hold the wafers horizontally on shoulders formed on the interior surfaces of the carrier. The same motion pattern of a translation followed by a rotation is typically used in the removal of the wafers from the cassetteless carrier.
In some processing applications, wafers are dipped in one or more baths for various purposes, during which the wafers must be held vertically. Typically, to orient horizontal wafers to a vertical position, the wafers are held in a cassette in which the back is open, allowing the wafers to protrude slightly. The cassette is tilted from horizontal to vertical and placed on its back on a flat surface, thereby pushing the protruding wafers upwardly to extend out of the cassette a sufficient distance for a robot arm or other transfer mechanism to grip the wafers. The robot arm then moves the vertically oriented wafers to the various baths. This method of orienting horizontal wafers to a vertical position, however, is not suitable for wafers held in cassetteless carriers.